This invention relates generally to atmospheric dispersion correctors, and more particularly, to an atmospheric dispersion corrector which is capable of providing dispersion correction over a broad spectral bandpass range as well as being utilized with telescopes having large apertures.
The effects of chromatic dispersion in the atmosphere or atmospheric dispersion (which lead to lateral color in the images of objects away from the zenith) are well known to astronomical observers. In the past the effect of atmospheric turbulence has been the limiting factor on design considerations, of, for example, telescopes and other astronomical instruments. In instances where the effects of atmospheric dispersion exceeded the blur due to atmospheric turbulence, special prisms were utilized to obviate these effects for observations at large zenith angles. However, in the past, no greater accuracy has been required in correcting dispersion than to reduce it to the level of the effects of turbulence at practical zenith distances.
With the introduction of techniques for overcoming turbulence effects, such as real-time compensation using active optics and speckle imaging, dispersion must now be corrected much more precisely in order to maintain the quality of the image. The requirement to eliminate the effects of atmospheric dispersion grow even more stringent as the size of the telescope and the spectral band covered increase. Ideally, the residual dispersion errors should be small compared to the Airy disc of the telescope, therefore demanding greater precision as the size of the telescope is increased.
Unfortunately, atmospheric dispersion correctors of the past and of the type disclosed by J. B. Breckinridge et al. in the publication entitled "Kitt Peak Speckle Camera", Applied Optics, Vol. 18, No. 7, Apr. 1, 1979, pgs 1034-1041 have provided the correction for only a relatively narrow potential band. Since it is desirable not only to correct over a relatively narrow spectral band but also over the entire visible band and beyond, a need exists for the development of an atmospheric dispersion corrector which is capable of operating with large telescopes over a broad spectral band. A further motivation for the development of a broadband corrector is the desire to develop a single device that can be used satisfactorily with a wide selection of image sensors from film to infrared detectors.